Transmission to glass
So "this just works" when rendering with Cycles, but Eevee requires a bit more setup.

Try the following settings:


Render → Screen Space Reflections ON
Render → Screen Space Reflections → Refraction ON
Material → Surface → Principled BSDF → Transmission 1.000
Material → Surface → Principled BSDF → Roughness [Cycles Only]
Material → Settings → Blend Mode OPAQUE [or ADDITIVE]
Material → Settings → Screen Space Refraction ON
Material → Settings → Refraction Depth PLAY WITH IT


You can also check out the documentation for:


Principled BSDF shader node
Eeve materials settings


You should get something like this in Render Mode, I didn't have the patience to model a teacup, so the default cube is all you get :)